Method to improve the efficiency of removal of liquid water from solid bulk fuel materials

ABSTRACT

The invention provides methods to efficiently reduce the water concentration of raw solid fuels, including low rank coals such as brown coal, lignite, subbituminous coal, and other carbonaceous solids. Efficiently drying these materials at low temperatures significantly reduces greenhouse gas emissions and allows the production of low-rank coals for gasification and liquifaction.

CROSS REFERENCE TO RELATED APPLICATION

This application claims the benefit of priority under 35 U.S.C. §119(e)to U.S. Provisional Patent Application No. 60/894,591 filed Mar. 13,2007, and to U.S. Provisional Patent Application No. 60/980,780 filedOct. 17, 2007, both of which are incorporated herein by reference.

FIELD OF THE INVENTION

This invention describes a method to efficiently reduce the moisturecontent of solid carbonaceous materials including brown coal, ligniteand subbituminous coal to produce premium-quality fuels.

BACKGROUND OF THE INVENTION

Low-rank coals (LRCs) are abundant in the United States and elsewhereand have the potential to provide an economic feedstock forgasification. LRCs typically contain between 25 and 45 wt % moisture inthe United States, and can be as great as 65 wt % in other countries.The high moisture content of LRCs has impeded their use as gasificationfeedstock because the gasification industry has identified an optimummoisture content not exceeding 15 wt %. If the feedstock moisture isgreater than 15 wt %, plant efficiency is impaired and economics may notbe viable. A LRC with high-moisture content emits more carbon dioxideduring utilization, on an equal energy basis, than low-moisturebituminous coal because the extra energy consumed evaporating moisturecontained in the LRC is not available for useful work. Efficiency isreduced and emissions are increased.

Coal gasification systems produce clean burning gas and liquid fuelsfrom solid fuels including coal and lignite. This technology isespecially attractive from an environmental standpoint because carbondioxide, believed to be an agent of global climate change, can beconcentrated and removed during processing. Clean burning syntheticnatural gas (SNG) is available for residential and industrial use.However, the yield of liquids such as diesel and naphtha that areproduced by gasification and liquefaction processes is severely impairedas the moisture of the feedstock increases above 12 wt %. The costsimposed by limiting feedstock to less than 12 wt % moisture severelyreduce the ability to use LRCs to produce petroleum liquids and gases.

Various methods have been employed by commercial entities and evaluatedby research laboratories to reduce the moisture content of LRCs.Virtually all require thermal energy to sufficiently heat the LRC toevaporate water and remove the superheated vapor from the dried solids.Some methods use an autoclave or pressure vessel to remove a portion ofthe water as a high-pressure superheated liquid.

The high-temperature (above 200° C.) thermal process uses an externalheat source to produce a working fluid such as air, combustion flue gas,steam, or other inert gases. Steam generators, combustors, stokerfurnaces, or gas or oil burners are required to heat the working fluidto the high temperature. The cost of these external energy sources canbe great, especially when environmental equipment is included to treatflue gases created during combustion.

In an attempt to reduce the cost of high-temperature thermal energy fromexternal heat sources, experiments have been conducted to extractlow-temperature (less than 100° C.) thermal energy from waste heatsources such as power plant condenser circuits, low-pressure steamcycles, flares, and thermal oxidizer flue gases.

The low-temperature drying methods require more time to evaporate agiven amount of water than the high-temperature methods. Therefore asubstantially larger drying vessel is required to provide the residencetime to evaporate the water. The expense of the larger drying vessel andancillary equipment is often greater than the benefit gained from usinga low-temperature waste energy source to heat the working fluid. CertainLRC's are heat sensitive and are easily oxidized during drying.Oxidation also reduces the useful energy contained in the dried product,and therefore reduces its commercial value. The rate of oxidation can bereduced by drying at relatively low temperature, preferably less than100° C.

Commercial drying systems require substantially more energy to evaporatethe water contained in LRCs than that required to evaporate an equalamount of liquid water held in direct contact with the working fluid.This fact can be explained by considering how liquid water is held bythe LRC:

-   -   1. Water residing on the surface of the LRC particle.    -   2. Water held in the interior pores of the LRC particle.

Water that is chemically bound to organic and inorganic molecules is notrelevant to the present invention because this form of water can only beremoved by thermal energy.

Water residing on the surface of the LRC particle is the easiest toevaporate because it comes into direct contact with the working fluid.Because little heat is transferred into the solid LRC particle duringthis operation, evaporation of this surface moisture is efficient andrapid. More energy is required to remove water held in pores of the bulkmaterial because a sufficient amount of thermal energy must be impartedby the working fluid to both evaporate water and heat the porous solidmaterial to evaporation temperatures.

Therefore the total energy required to evaporate liquid water held byLRC is the sum of the energy required to evaporate and remove waterresiding on the surface and within the pores of the material. The sum isalways greater using existing thermal drying systems than that requiredto evaporate the equivalent amount of liquid water from the surface of asolid in contact with a working fluid.

SUMMARY OF THE INVENTION

The present invention improves the efficiency of thermal drying methodsby evaporating liquid water that was transferred to the surface of theparticle from interior pores during compaction by mechanical forces.Increased efficiencies result because water residing on the surface thatis direct contact with the working fluid can be evaporated with lesstime and energy than water residing in the material's internal pores.The present invention transforms LRC to remove moisture, and in agasification application, improves the gasification characteristics ofraw LRC feedstock.

Most LRCs have porous structures that contain liquid water and othertightly held materials. The process described in U.S. patent applicationSer. No. 11/380,884, filed Apr. 28, 2006 (U.S. Patent Publication No.2007-0023549 A1), which is incorporated herein by reference, compressesraw material to reduce pore volume and express a significant proportionof the water contained in the pore volume. The high compaction forcespermanently deform the raw feed to produce a nearly solid impermeableproduct that is less susceptible to reabsorb water and oxygen. Thistransformation, when conducted on finely sized raw feed materials, hasproven useful to both reduce the moisture content of feedstock andmodify the texture of the material.

In the present invention, high compaction forces are continuouslyimparted at ambient temperature to the feed material. Sufficient forceis used to collapse the material's porous structure and force theexpelled water to the surface of the compacted material. The wetcompacted material is then fed to a low-temperature or ambienttemperature-drying device where a substantial proportion of the water isevaporated from the surface of the material. As an additional benefit,the present invention, by being more efficient, can dry materials atambient temperatures that are too low to be economically practical withconventional thermal drying systems that do not treat the feed prior todrying. Operating the present invention at ambient temperatures willprovide additional desirable cost advantages to the utility andgasification industries, among others, by allowing production and use oflow cost dried LRC products. Benefits include, via increased dryingefficiencies, reducing the amount of carbon dioxide and other gaseouspollutants such as sulfur dioxide and nitrous oxides released duringproduction and utilization. Providing the opportunity to economicallyuse domestic LRC resources to produce motor fuels will substantiallyreduce use of foreign oil. Thus the present invention proves beneficialin three ways: economically reducing moisture content below 15 wt %,forming a briquette that has predictable reaction kinetics with steamand oxygen, and providing a strong material that can support the weightof burden held in the gasification reactor.

The present invention provides processing methods to efficiently processraw bulk materials into low-moisture content products. The presentinvention includes the following subsystems:

-   -   1. Raw solid fuel preparation.    -   2. Material compaction.    -   3. Working fluid management.    -   4. Drying.    -   5. Dust collection.    -   6. Optional secondary compaction means to form the material into        desired shapes, as may be required by specific applications

Raw materials, such as LRC's are often mined and crushed to 50 mm topsize, a size typically traded worldwide. The raw materials are typicallycarbonaceous materials and particularly carbonaceous fuels that mayinclude brown coal, lignite, subbituminous coal, waste coals andmixtures of these materials. The present invention receives thiscarbonaceous material and crushes it to pass a 5 mm screen or othersimilar size, depending on the application. Preferably, the feedstock iscrushed to reduce its nominal top size to between 0.1 mm to 6 mm, andmore preferably to a nominal top size of about 0.5 mm. The presentinvention processes all of the feed material, thus achieving greaterrecovery of resources than other drying techniques that must remove andpotentially discard finely sized materials prior to processing.

The feed material is then compacted using an applied mechanical forcesufficient to deform the feedstock to reduce its pore volume.Preferably, the force applied is in the range of between 5,000 lb/in²and 50,000 lb/in², and more preferably the applied force is about 30,000lb/in². The prepared feed material may be fed to compactors, such asroll presses, that exert high pressures on the material. The pressuresexerted by the roll presses may range as high as 275,000 kPa per cm ofroll width. The material is physically transformed under the pressure tocollapse the porous structures that are present in most LRC's. The porescontain water, which collapse under pressure, forcing the water from thepores to the surface of the material. In some cases, sufficient water ispresent in the bulk starting material to be removed from the compressedmaterial as a liquid and be carried away from the processing stream.Separating liquid water from the material prior to drying reduces thethermal load on the system.

The wet compacted material is transported to low-temperature processing,such as an indirect rotary dryer to evaporate the liquid water presenton or near the surface of the compressed particles. Drying rates ofcompacted materials can be many times greater than drying rates of theraw material before compaction. The reason for the increased drying rateis the water expressed from the pores is in direct contact withunsaturated gas (“working fluid” as defined below) passing over thematerial. Increasing drying rates at low temperatures provides theoperator with several benefits not offered by traditional processes. Forexample, smaller and less costly equipment can be used to achieve thedesired capacity. If costs do not constrain the operation, greatercapacity can be achieved with compaction. Lower working temperatures canbe used to dry heat-sensitive materials, thereby avoiding orsubstantially reducing oxidation and product deterioration.

In another embodiment of the invention, a covered open stockpile can beused to gently but efficiently dry compacted material. Experimentsreveal that the stockpiled material can be well managed becauseoxidation rates of LRC's can be greatly reduced by compaction.

The low-temperature drying process requires a source of unsaturated gas(working fluid) to heat the compacted material and transport thesuperheated water vapor away from the dried material. Heat sources canrange from ambient air to gas supplied from electric heaters, gas- andother fossil-fired combustors, and waste heat available from existingindustrial processes such as power plants. Management of the heat sourcecan be affected by readily-available commercial equipment.

Spent working fluid, containing the water removed by evaporation, oftencontains dust that must be collected and processed to meet environmentalregulations. Experiments by the present inventors have confirmed thatthe spent working fluid produced during low-temperature drying does notcontain significant organic vapors to require additional collection orthermal treatment. Substantial cost savings result. In one embodiment,collected dust can be introduced, or re-introduced, to the compactionoperation to increase product yield.

Dried product may be transformed into desired shapes, such asbriquettes, that can be readily handled, stored, and transported by railor ship to distant customers. The formed shapes may be desired toprovide favorable material handling properties including acceptable bulkdensity, reduced breakage and dust generation, and resistance tooxidation during storage.

Numerous gasification processes have been identified and developed. Onesuch process that has commercial application processes solid feedstockto produce carbon monoxide and hydrogen (referred to as syngas) and slagas a waste product. The process vessel resembles a tall vertical tankthat accepts feed at the top of the vessel. Oxygen and steam areinjected near the bottom of the vessel (reaction zone) to createexothermic reactions that produce syngas. The feed slowly descends thevessel as material is consumed in the reaction zone. New feed iscontinuously added to make up volume consumed. The efficiency of thereactions depends on the feed material maintaining sufficient mechanicalstrength to support its bulk weight and porosity to allow gases to flowupward and out of the reaction vessel. An ideal feed therefore containsan optimum moisture content (less than 15 wt %), and produce acarbonized material (coke) with exceptional mechanical strength andstability. In addition, the texture (grain size) of the feed material isspecified to provide the desired reaction rate between the coke, oxygen,and steam.

Briquettes produced from LRC by the processes of the present inventionhave proven to be beneficial as a gasifier feedstock because of itsideal moisture content (8-15 wt %), mechanical strength after coking(greater than 600 lb/in2 compressive strength at ambient temperature),and moderate rate of reaction with steam at high temperature.

The operating conditions operating conditions of the processes of thepresent invention can be adjusted to provide briquette products with thespecified moisture content, strength, and texture.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic drawing of a low-temperature drying processintegrated into a typical fossil-fired power plant operation in which asource of waste heat is available to heat the working fluid.

FIG. 2 shows a schematic drawing of low-temperature drying process thatcan be independently sited where no waste heat is available. Ambient airprovides the working medium.

FIG. 3 shows a schematic drawing of low-temperature drying process thatcan be independently sited and uses an external heat source to providewarm air for drying.

FIG. 4 shows a schematic drawing of an ambient-temperature dryingprocess that can be independently sited where material is stored in acovered stockpile. The stockpile is managed to accept compacted materialon a continuous basis and be reclaimed as required.

FIG. 5 is a graph showing the results of a study comparing the relativedrying rates of raw lignite and compacted lignite.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides a novel method to treat solidcarbonaceous materials such as lignite and subbituminous coal used tofire boilers, combustors, stokers, and to feed coal gasifiers. Thismethod takes advantage of the fact that a significant proportion of thewater contained in pores of low-rank coal (often as much as 74% of thetotal water) can be efficiently evaporated without the difficulties ofthe conventional thermal drying systems. Conventional drying operationsmust heat the solids to evaporation temperatures to remove water held inthe interior of the material. Because the rate of drying is greater withthe present invention, lower temperatures can be efficiently used,significantly reducing material oxidation.

The method continuously compacts and collapses the porous material toexpress water held in pores, and transfers the expressed water to thesurface of the processed material. Water residing on the surface isefficiently evaporated in the presence of the working fluid. By avoidingthe difficulties associated with heat and mass transfer into and out ofa particle, the present invention provides the superior heat and masstransfer only available when water is placed in direct contact with aworking fluid. The efficiency gains can make both ambient-temperatureand elevated-temperature drying systems practical in many applications.

The present invention includes the following subsystems:

-   -   1. Raw solid fuel preparation.    -   2. Material compaction.    -   3. Working fluid management.    -   4. Drying.    -   5. Dust collection.    -   6. Optional secondary compaction to form the dried product into        desired shapes, as may be required for certain commercial or        industrial applications.

Each of these subsystems is described in detail below.

Raw Solid Fuel Preparation

The raw solid fuel preparation subsystem receives crushed material oftraditional trade top size, typically about 50 mm. In one preferredembodiment, the minus-50 mm raw solid fuel is comminuted by a hammermill, roll crusher, or other appropriate device to produce a product ofapproximately 5 mm top size. The optimum particle size required toprovide the desired compaction properties is experimentally determinedfor a particular application and feed source.

However, feed to the compactor may have a top size that typically variesbetween about 0.1 mm and about 19 mm. Preferably, the top size is about0.5 mm. The crushed material may include carbonaceous materials such asbrown coal, lignite, subbituminous coal, waste coals and mixtures ofthese materials. Preferably, this raw feedstock contains between about15 weight percent moisture and about 65 weight percent moisture, andmore preferably about 35 weight percent moisture. Preferably, thetemperature of this raw feedstock is between about 17° C. and about 66°C., and more preferably the feedstock is at ambient temperature.

Primary Material Compaction

The prepared bulk raw material is compacted with sufficient force tomobilize and transfer waters held in fractures, voids, and pores fromthe interior of the solid particle to the surface of the solid particle.Preferably, the compaction of the pre pared bulk raw material isconducted in a continuous manner. The compaction force produces apressure of between about 5000 lb/in² and about 50000 lb/in², and morepreferably the compaction force produced is about 30000 lb/in².

In the preferred embodiment, a roller press is used to compact the feedmaterial using a specific roll force between about 5 kN/cm and about 150kN/cm of roll width. Water driven from the interior to the surface ofparticles by these compaction forces therefore becomes readily availablefor contact with a working fluid.

Working Fluid Management

The working fluid can be unsaturated air, nitrogen, inert gas, flue gas,superheated steam, or other substances that are compatible with thedried material. The working fluid management system generates asubstance containing less than 100% relative humidity. In a preferredembodiment, the substance is air containing less 100% relative humiditythat is collected and contacted with the wet material using naturalconvection, fans, or blowers. In these cases, the entire drying systemis independent of external heat sources. The material can contact theworking fluid in stockpiles and drying vessels such as a rotary dryer.In another embodiment, the working fluid can be heated by an externalsource. Supplied heat may be transferred to the working fluid by a heatexchanger. The heat exchanger is configured to suit the application.Sources of external heat may include, for example, condenser coolingwater, flue gas desulfurization sludge, gasifier cooling water, syngascooling water, heat recovery steam generator, or other forms of heatthat would otherwise be rejected to the environment. In yet anotherembodiment, the working fluid generated by an external heat source canbe hot flue gas that is tempered with air, or other material that is ata lower temperature than the combustion gas. In yet another relatedembodiment, a purpose-built boiler or combustor can be used to heat theworking fluid.

Drying

The compacted product, usually in flake or pellet form, is transferredto a vessel where feed particles can be efficiently contacted with theunsaturated working fluid. In a preferred embodiment that works withcoal or other heat-sensitive applications, the drying vessel is anindirect rotary dryer. Indirect rotary dryers transfer heat into the wetcompressed material in two ways. First, heat is transferred byconvection. This is accomplished by passing hot working fluid over thewet material. Second, heat is transferred by conduction by contactingthe wet compressed material with a hot surface (shell of the rotarydryer). Both sources of heat evaporate water. In other applications thatwork with materials that are not heat sensitive, a direct rotary dryermay be used. Direct dryers use heat supplied by the hot working fluidalone, and do not heat the material by conduction. The working fluidused in a direct dryer is typically hotter than the working fluid usedin an indirect rotary dryer.

In another embodiment, unsaturated air can be directed across astockpile of compacted material. Fans or natural convection can used toaccelerate the air to increase the rate of drying.

In another embodiment, material can be conveyed on a vibrating panconveyor fitted with a perforated screen deck. Working fluid entersupward though the perforations and flows past the conveyed material. Theconveyor device is sufficiently long to provide the required residencetime to dry the material. Saturated vapor is removed from the top of theconveyer. Additional methods including fluid bed dryers and othervessels of commercial configuration are available. The present inventionis not limited to the type of style of drying vessel as long as it iscompatible with the process material.

Dust Collection

Vapors emanated from the dryer often contain dust that must be removedbefore venting to the atmosphere. Standard dust separation andcollection devices such as electrostatic precipitators, bag houses orwet scrubbers may be used to separate fine particles from water vaporsas dictated by the application. Collected fine particles may be recycledto the compaction subsystem as desired, so that all, or nearly all, feedmaterial is processed without waste.

Secondary Material Compaction

Applications that require the finished product to be of a specifiedshape, such as a briquette, can be accommodated by compacting the driedproduct as described above. Formed products are typically used where thedried material is transported, or used in stoker furnaces where a coarseparticle size distribution is required.

In instances in which a shaped final product is desired, the product ispreferably a briquette of ovoid shape with a minor dimension of at leastabout 6 mm, but less than about 100 mm, and more preferably having aminor dimension of about 50 mm. These shaped products are preferablyformed bulk materials having a void space of between about 12 volumepercent and about 60 volume percent, and more preferably having a voidspace of about 30 volume percent void space. Preferably, the shapedproducts are formed such that upon being subjected to coking conditions,they form coke that has a compressive strength between about 100 lb/in²and about 2,000 lb/in², and more preferably a compressive strength ofabout 800 lb/in². Preferably, the shaped products have a total moisturecontent between about 7 weight percent and about 17 weight percent, andmore preferably a total moisture content of about 12 wt %.

FIG. 1 shows a schematic of the overall system of a preferred embodimentof the invention. A source of raw solid fuel (1) supplies material (2)to the raw solid fuel comminution circuit (3) where the feed is crushedand sized. The prepared raw feed (4) and collected dust (12) are feed tothe compaction circuit (5) where they are compressed under high pressureto force water from its internal pores to produce a flake product withwater adhering to the surface of the compacted material (6). Thecompacted material is fed to the dryer (7) where it is mixed with heatedair (19), evaporating the water residing on the surface of the compactedmaterial. The resulting vapors and dust (8) are passed to a dustcollection circuit (9) where the dust and water vapor are separated.Dust-free vapor (10) is vented to the atmosphere (11). Dust (12) isconveyed to the compaction circuit. Dryer product (13) containingsubstantially less moisture than the feed, but within the applicationproduct specifications, is conveyed to a dried product storage point(14) where it is available for use or additional processing. A source ofwaste heat (15) capable of supplying sufficient power to satisfy theevaporative load provides a hot flow input (16) and accepts a hot flowreturn (17). A sufficient temperature drop exists between the input andreturn flows to impart the required energy to the working fluid (21). Anambient air source (20) provides the cool working fluid (21) to the heatexchanger (18) where it is heated to a specified temperature by thecirculating hot in and hot out flows. The heated working fluid (19)passes to the dryer where it contacts the wet feed material.

FIG. 2 shows a schematic of the overall system of a preferred embodimentof the present invention. A source of raw solid fuel (21) suppliesmaterial (22) to the raw solid fuel comminution circuit (23) where thefeed is crushed and sized. The prepared raw feed (24) and collected dust(212) is feed to the compaction circuit (25) where it is compressedunder high pressure to force water from the feed's internal pores toproduce a flake product with water adhering to the surface of thecompacted material (26). The compacted material is fed to the dryer (27)where it is mixed with unsaturated ambient-temperature air (215) thusevaporating the water residing on the surface of the compacted material.The resulting vapors and dust (28) are passed to a dust collectioncircuit (29) where dust and water vapor is separated. Dust-free vapor(210) is vented to the atmosphere (211). Dust (212) is conveyed to thecompaction circuit. Dryer product (213) containing substantially lessmoisture than the feed, but within the application productspecifications, is conveyed to a dried product storage point (214) whereit is available for use or additional processing. A source ofambient-temperature air (215) is fed into the dryer.

FIG. 3 shows a schematic of the overall system of a preferred embodimentof the invention. A source of raw solid fuel (31) supplies material (32)to the raw solid fuel comminution circuit (33) where the feed is crushedand sized. The prepared raw feed (34) and collected dust (312) is feedto the compaction circuit (35) where it is compressed under highpressure to force water from the feed's internal pores to produce aflake product with water adhering to the surface of the compactedmaterial (36). The compacted material is fed to the dryer (37) where itis mixed with heated air and flue gas (322) thus evaporating the waterresiding on the surface of the compacted material. The resulting vaporsand dust (38) are passed to a dust collection circuit (39) where dustand water vapor are separated. Dust-free vapor (310) is vented to theatmosphere (311). Dust (312) is conveyed to the compaction circuit.Dryer product (313) containing substantially less moisture than thefeed, but within the application product specifications, is conveyed toa dried product storage point (314) where it is available for use oradditional processing. A source of ambient air (319) provides combustionair (320) and tempering air (321) to the process. A source of fuel (315)is supplied (16) to a furnace (317) where it is combusted to provide hotflue gas (318). The flue gas is mixed with tempering air (321) toprovide a warm gas (322) of the specified temperature for dryingpurposes.

FIG. 4 shows a schematic of a preferred embodiment of the invention. Asource of raw solid fuel (41) supplies material (42) to the raw solidfuel comminution circuit (43) where the feed is crushed and sized. Theprepared raw feed (44) is feed to the compaction circuit (45) where itis compressed under high pressure to force water from the feed'sinternal pores to produce a flake product with water adhering to thesurface of the compacted material (46). The compacted material isstacked out in a covered stockpile (47). A source of ambient,unsaturated air (48) is available to sweep (49) over the stockpiledmaterial thus evaporating the water residing on the surface of thecompacted material. The resulting vapors (410) are released as a gas tothe atmosphere (411). Dried product (412) containing substantially lessmoisture than the feed, but within the application productspecifications, is reclaimed to a dried product storage point (413)where it is available for use or additional processing.

Additional objects, advantages, and novel features of this inventionwill become apparent to those skilled in the art upon examination of thefollowing examples thereof, which are not intended to be limiting.

EXAMPLES Example 1

A detailed study of lignite (high-moisture lignite from North Dakota)was undertaken to assess the relative drying rates of raw material andcompacted product. Experiments were conducted on materials spread out ona flat tarpaulin at ambient conditions. Samples of raw lignite andcompacted lignite were taken periodically from the spread out materialand assayed for total moisture. The measured moisture values werenormalized as percent of the total water evaporated to compare theresults on an equal basis. Drying conditions were 31° C., and 23%relative humidity. Results are plotted in FIG. 5.

These results demonstrate the increased drying rates possible bycompacting the raw lignite. Table 1 summarizes the ratio of drying ratesbetween raw and compacted lignite processed at ambient conditions of 31°C., 23% relative humidity.

TABLE 1 Ratio of Relative Drying Rates for North Dakota Lignite DryingTime, % Moisture Removed hr Raw Compacted Ratio 0.5 4 16 4.0 1.0 9 222.4 1.5 13 26 2.0 2.0 16 28 1.8

Example 2

A detailed study of one LRC (high-moisture lignite from South East Asia)was undertaken to assess the relative drying rates of raw material andcompacted product processed by an indirect rotary dryer (180 mmdiameter×3000 mm long). The heated portion of the drying tube was 2000mm long, the cooling zone was 600 mm long, and the feed zone was 400 mmlong. Test conditions were identical for the compacted and rawmaterials. The results are summarized in Table 2.

TABLE 2 Rotary Indirect Dryer Test Results Compacted Raw Test ParameterMaterial Material Feed moisture, wt % 45 46 Product moisture, wt % 16 38Residence time, min 20 20 Sweep gas temperature, at 130 130 feed point,° C. Shell temperature, ° C. Less than 110 Less than 110 Maximummaterial Less than 100 Less than 100 temperature, ° C. Sweep gas flowrate, L/min 700 700 Material feed rate, kg/min 10 10

These data show the compacted material dries to a lower moisture contentthat is about half that of the raw material under identical dryingconditions. The increased drying rate afforded by compaction effectivelydoubles the capacity of the drying equipment. If cost savings are moreimportant than capacity, the cost of the drying equipment will be half.

Example 3

An experiment was conducted to measure the relative drying rates ofSouth East Asia lignite held under warm, moist conditions that would beexpected in a covered stockpile located in non-condensing, warm, humidtropical climates. Table 3 lists results.

TABLE 3 Moisture Content of Lignite Stored in Warm, Humid Atmosphere 30°C., >60% Relative Humidity Raw Lignite Compacted Time, Moisture, LigniteMoisture, hrs wt % wt % 0 40 43 48 36 37

These test data show that the compacted material lost 50% more moisturethan the raw material in 48 hours.

Example 4

Samples of lignite produced from North Dakota were processed by the GTLEprocess to form briquettes of low moisture content. These briquetteswere then processed at high temperature and gas conditions that aretypical of those found in the reaction zone of a solid feed gasifier.

The compressive strength of the briquettes and associated coke producedfrom the gasification conditions were measured. Tests were alsoconducted on briquettes formed from North Dakota lignite by standardindustrial processes typically used to form home heating fuels and otherindustrial products. Test results are listed in Table 4.

TABLE 4 Compressive Strength of Briquettes and Coke Produced from LRCsBriquette Compressive Strength, Sample Moisture, lb/in² Description wt %Briquette Coke Process Method North Dakota 16.3 1,405 711 PresentInvention Lignite #5 A North Dakota 10.9 944 676 Present InventionLignite #5 B North Dakota 12.0 1,211 898 Present Invention Lignite #6 ANorth Dakota 9.98 767 755 Present Invention Lignite #6 B North Dakota8.24 735 506 Present Invention Lignite #6 C German Lignite 10.81 n/a 247Industrial Process

These results demonstrate the increase of compressive strength from 247lb/in² for coke produced from briquettes formed from industrialprocesses to over 500 lb/in² for coke produced from briquettes formed bythe present invention.

The foregoing description of the present invention has been presentedfor purposes of illustration and description. Furthermore, thedescription is not intended to limit the invention to the form disclosedherein. Consequently, variations and modifications commensurate with theabove teachings, and the skill or knowledge of the relevant art, arewithin the scope of the present invention. The embodiment describedhereinabove is further intended to explain the best mode known forpracticing the invention and to enable others skilled in the art toutilize the invention in such, or other, embodiments and with variousmodifications required by the particular applications or uses of thepresent invention. It is intended that the appended claims be construedto include alternative embodiments to the extent permitted by the priorart.

What is claimed is:
 1. A method of treating a solid carbonaceousmaterial comprising: compacting a solid carbonaceous material under aforce of at least about 5000 lb/in² to form a compacted carbonaceousmaterial; and, contacting the compacted carbonaceous material with aworking fluid, wherein the working fluid causes evaporative drying ofthe compacted carbonaceous material to form a dried carbonaceousmaterial.
 2. The method of claim 1, wherein the solid carbonaceousmaterial is selected from the group consisting of brown coal, lignite,subbituminous coal and mixtures of these materials.
 3. The method ofclaim 1, wherein the solid carbonaceous material has a top size betweenabout 0.1 mm and about 6 mm.
 4. The method of claim 1, wherein the solidcarbonaceous material has a moisture content between about 15 weightpercent and about 65 weight percent.
 5. The method of claim 1, whereinthe solid carbonaceous material has a temperature between about 17° C.and about 66° C.
 6. The method of claim 1, wherein the force is betweenabout 5000 lb/in² and about 50000 lb/in².
 7. The method of claim 1,wherein the working fluid is selected from the group consisting ofunsaturated air, nitrogen, inert gas, flue gas, superheated steam andmixtures of these fluids.
 8. The method of claim 1, wherein thecontacting comprises applying the working fluid to the compactedcarbonaceous material in at least one of a stockpile of the compactedcarbonaceous material and a rotary dryer containing the carbonaceousmaterial.
 9. The method of claim 1, wherein the contacting comprisescontacting the compacted carbonaceous material on a conveyor with aworking fluid flowing past the conveyed material.
 10. The method ofclaim 1, further comprising collecting dust created in the contactingstep and returning the collected dust to a solid carbonaceous materialfor the compacting step.
 11. The method of claim 1, further comprisingcompacting the dried carbonaceous material to form a shaped compactedmaterial.
 12. The method of claim 11, wherein the shaped compactedmaterial is a briquette of ovoid shape with a minor dimension betweenabout 6 mm and about 100 mm.
 13. The method of claim 11, wherein theshaped compacted material has a moisture content between about 7 weightpercent and about 17 weight percent.